Optimization procedure for electric propulsion engines
De Bellis, John J.
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This thesis addresses the optimization of all types of space electrical propulsion thrusters. From the Langmuir-Irving payload mass fraction formulation, a "dual-optimum" solution is defined, yielding a minimum overall mass for a specified payload consistent with minimum transfer time. This solution fixes the ideal payload mass ratio (m(pl / m(o)) at a value of 0.45, establishing the ratios of effective exhaust velocity (v / V(c)) and incremental change of vehicle velocity (deltau / V(c)) to characteristic velocity at 0.820 and 0.327 respectively. The characteristic velocity (V(c)) includes thrust time as well as engine efficiency (eta(t)) and specific power (alpha). A range of mass ratios from 0.35 to 0.55 is used in order to allow the system designer some flexibility while remaining close to optimal. Nine examples are presented which demonstrate that mission profiles can be optimized by profile-to-thruster matching. A comprehensive list of currently available electric propulsion engines is provided. This list details important parameters such as the specific power, which "sizes" an engine in terms of power provided to the thruster at the cost of additional mass. Allowance is, also made for a fuel tank mass penalty, and examples show that this can also noticeably influence the optimum design.